Seedling Diseases: Damping Off & Late Blight

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Questions and Answers

What is the recommended management practice for preventing the spread of leaf curl disease before planting new crops?

Use chemical fertilizers

Rogue out and destroy diseased plants (correct)

Plant without clearing previous crops

Inoculate with severe virus strains

Which factor is likely to increase the incidence of leaf curl disease during the kharif season?

Reduction of watering

Presence of weed hosts (correct)

Dry weather conditions

Soil fertilization

What is a symptom of leaf curl disease caused by Tobacco leaf curl virus?

Withering of stems

Leaves becoming transparent

Crinkling and curling of leaves (correct)

Roots being stunted

What method is NOT recommended for managing the Tobacco leaf curl virus?

Leave weed hosts undisturbed Signup and view all the answers

Which of the following best describes how the Tobacco leaf curl virus spreads?

By seed and through thrips Signup and view all the answers

What is the appearance of leaf spots caused by Early Blight of Tomato?

Round, brown spots with target-like concentric rings and yellowing tissue Signup and view all the answers

What happens to the stems of seedlings infected with Early Blight?

They turn brown, sunken, and dry, leading to collar rot Signup and view all the answers

Which environmental conditions favor the development of Early Blight?

Moderate to warm temperatures with high humidity Signup and view all the answers

What is the recommended treatment for Early Blight of Tomato?

Apply copper fungicide spray weekly Signup and view all the answers

What is a characteristic symptom of fruit infected by Early Blight?

Leathery, black spots with raised concentric ridges Signup and view all the answers

How is Tomato mosaic virus primarily spread?

By leaf contact and implements used in cultural operations Signup and view all the answers

Which symptoms are indicative of Tomato mosaic virus infection?

Light and dark green mosaic mottle with distorted crinkled leaves Signup and view all the answers

Which of the following factors does NOT contribute to the survival of Early Blight?

Exposure to direct sunlight Signup and view all the answers

What stage is characterized by the complete rotting of seedlings just before they reach the soil surface?

Pre-emergence phase Signup and view all the answers

Which environmental condition significantly increases susceptibility to damping off in tomato seedlings?

Cloudy, wet weather and low light Signup and view all the answers

What is the main cause of damping off disease in tomato seedlings?

Fungal infection Signup and view all the answers

What management practice can help prevent damping off in tomato seedlings?

Use fungicide-treated certified seeds Signup and view all the answers

Which of the following pathogens is NOT mentioned as a cause of damping off in tomato plants?

Fusarium Signup and view all the answers

What commonly observed symptom indicates a post-emergence damping-off phase?

Collapsing of seedlings Signup and view all the answers

How should seedlings be spaced to ensure proper aeration and prevent damping off?

With at least 5 cm (2 inches) between each seed Signup and view all the answers

What is the effect of excess nitrogen application on tomato seedlings?

Can lead to susceptibility to damping off Signup and view all the answers

What characteristic is common in the lesions caused by Phytophthora infestans on tomato leaves?

They begin as small necrotic spots. Signup and view all the answers

What is the primary mode of reproduction for Phytophthora infestans?

Asexual reproduction by producing sporangia. Signup and view all the answers

Under what conditions do zoospores of Phytophthora infestans typically emerge?

Cool, wet conditions. Signup and view all the answers

Which of the following management strategies is effective against Phytophthora infestans?

Avoiding sprinkler irrigation. Signup and view all the answers

What type of pathogen is Phytophthora infestans classified as?

Oomycete. Signup and view all the answers

Which statement about sporangia of Phytophthora infestans is true?

They can be produced on infected crop residues. Signup and view all the answers

What is a major challenge in controlling the spread of Phytophthora infestans in California?

Resistance to Metalaxyl is widespread. Signup and view all the answers

How do zoospores infect host plants?

By encysting after swimming on the plant's surface. Signup and view all the answers

Study Notes

Damping Off of Seedlings

Caused by fungi: Pythium, Rhizoctonia, or Phytophthora
Affects tomato seeds, stems, and roots
Common in humid conditions, especially with cold, wet soil
Young seedlings are most susceptible
Affects seedlings before (pre-emergence) and after (post-emergence) they reach the soil surface
Pre-emergence: Seedlings rot, don't reach the surface
Post-emergence: Soft, water-soaked tissues at ground level, leads to toppling over
Spread by air, water, and soil
Favourable conditions: first three weeks after sowing, heavily infested soil, overwatering, poor drainage, overcrowding, poor ventilation, excess nitrogen, stressful environmental conditions, and presence of pathogenic nematodes

Tomato Late Blight

Caused by Phytophthora infestans
Affects leaves, stems, and fruit
Leaf lesions: small, dark spots that become brown, may have a yellow border
Stem lesions: dark brown, with well-defined edges
Fruit lesions: brown, firm, may have a rough surface
Survival: infected fruits, seeds, crop residue, and other crops
Spread: wind, rain splashes, and heavy dew

Early Blight of Tomato

Caused by Alternaria solani
Affects: leaves, stems, and fruit.
Leaf symptoms: dark spots, round, brown, target-like concentric rings, yellow tissue around spots, brown and dead leaves
Stem symptoms: infection at or above soil line, brown, sunken, dry, stem wilting and death
Fruit symptoms: leathery, black spots, raised concentric ridges, fruit drop
Survival: infected plants, seeds
Spread: water, wind, insects, animals

Tomato Mosaic Virus

Causes mosaic mottling, stunted growth, leaf distortion
Symptoms depend on the strain, can include yellowing, leaf mottling, streaking, necrosis, and fruit browning
Spread: seedborne, sap-transmissible, human and animal contact, implements, leaf contact
Survival: seedborne, in contaminated tools, equipment, and plant debris

Leaf Curl (Tobacco Leaf Curl Virus)

Causes crinkling and curling of leaves, stunted plants, reduced internode length, puckering, leaf outgrowths
Spread: whiteflies, seedborne
Survival: weed hosts

Favourable Conditions for Other Diseases:

Tomato Yellow Leaf Curl Virus: Rainy days, weed hosts, other legume hosts, chillies, and petunia
Tomato Late Blight: Cool, wet conditions, heavy dew

Management Strategies

Damping Off: Avoid shaded, humid places, select well-draining nursery sites, elevate seed beds, use disease-free seedlings, space seeds and stake plants, avoid overwatering, irrigate early in the day, use fungicide-treated seeds, seed treatment with Thirum (3gm/kg), foliar spray with Metalaxyl (0.2%) during cloudy weather
Tomato Late Blight: Resistant varieties, remove volunteer tomato plants and nightshades, avoid sprinkler irrigation, fungicides (Mancozeb + Cymoxanil @1.5g/l, Azoxystrobin + Difenoconazole @1ml/l, Mancozeb 75WP @2.5g/l)
Early Blight: Remove and destroy infected leaves, copper fungicide spray (once a week and after rain), chlorothalonil, Mancozeb or Maneb
Tomato Mosaic Virus: Destroy collateral hosts, rouge out diseased plants, use virus-free seeds, cross-protection, field workers should avoid tobacco products
Leaf Curl: Spray Monocrotophos (15, 25, 45 DAS)
Tomato Yellow Leaf Curl Virus: Rogue out infected plants (within 30 days), remove weed hosts, spray Monocrotophos or Methyl demeton (500 ml/ha at 30 and 45 days after sowing)

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Description

This quiz explores the causes and effects of damping off and late blight in seedlings, particularly focusing on tomatoes. It covers the fungi responsible, symptoms, environmental conditions that promote these diseases, and their impact on young plants. Test your knowledge on these critical issues in plant health.